Ratios: (common print sizes bolded)

2-3 can be printed as 2x3, 4x6, 6x9, 8x12, 10x15, 12x18, 14x21, 16x24, 18x27, 20x30, 22x33, 24x36 ...

4-5 can be printed as 4x5, 8x10, 12x15, 16x20, 20x25, 24x30, 28x35, 32x40, 36x45, 40x50 ...

If you try to print using the wrong ratio, most print labs will chop off the sides or the top/bottom of the photo.

Many photo labs will overprint a photo by 1/4 to 1/3 of an inch so that the image extends the sheet without any white space showing (called borderless). I try to account for this in my poster designs, but sometimes the paper does not align correctly when going through the printers. Feel free to resize the photos to allow for the width of your frame.